Human placental membrane (e g amniotic membrane) has been used for various types of reconstructive surgical procedures since the early 1900s. The membrane serves as a substrate material, more commonly referred to as a biological dressing or tissue graft. Such a membrane has also been used for ophthalmic procedures and more recently for dental regenerative procedures, treating ulcers, and as an adhesion barrier. Typically, the membrane is either frozen or dried for preservation and storage.
Placental tissue is typically harvested after an elective Cesarean surgery. The placenta is composed of the amniotic sac and sometimes is meant to include the umbilical cord and amniotic sac. The amniotic sac contains the amniotic fluid and protects the fetal environment.
The amniotic sac, commonly referred to as the amniotic membrane, has two primary layers of tissue, amnion and chorion. Amnion is the innermost layer of the amniotic sac and is in direct contact with the amniotic fluid. Histological evaluation indicates that the membrane layers of the amnion consist of a single layer of epithelium cells, thin reticular fibers (basement membrane), a thick compact layer, and a fibroblast layer. The fibrous layer of amnion (i.e., the basement membrane) contains collagen types IV, V, and VII, and cell-adhesion bio-active factors including fibronectin and laminins.
Placental tissue, such as amnion membrane, provides unique characteristics when used for surgical and wound-healing procedures, including providing a matrix for cellular migration/proliferation, providing a natural biological barrier, is non-immunogenic, and contains numerous bio-active molecules. Placental tissue can be used as a membrane to assist in tissue regeneration and improved healing outcomes in numerous applications. The amnion has the capability to self-adhere or, in the alternative, is susceptible of being fixed in place using different techniques, including fibrin glue or suturing.
Difficult-to-heal wounds are a common problem in hospital and clinical situations. Chronic wounds include, for example, venous stasis ulcers, decubitus ulcers and diabetic ulcers, and the like. Acute wounds include, for example, burns, skin graft donor sites, skin graft recipient sites, abrasions, and the like. In either case, the initial injury initiates inflammation, an early stage of the healing process. Mediators involved in inflammation, such as histamine, increase capillary permeability so that white blood cells can escape and the blood vessels leak more fluid. The excess fluid enters the wound where it forms the basis of what is referred to as an exudate. Exudate is derived from fluid that has leaked out of blood vessels and closely resembles blood plasma. Fluid leaks from capillaries into body tissues at a rate that is determined by the leakiness (permeability) of the capillaries and the pressures (hydrostatic and osmotic) across the capillary walls.
Exudate supports healing and a moist wound environment. The main role of exudate is to facilitate the diffusion of vital healing factors (e.g., growth and immune factors) and the migration of cells across the wound bed. It also promotes cell proliferation, provides nutrients for cell metabolism, and aids autolysis of necrotic or damaged tissue. In a wound that is not healing as expected, however, exudate production may continue and be excessive due to ongoing inflammatory or other processes. Although a moist environment is necessary for optimal wound healing, conditions of extreme wetness or dryness may adversely affect healing.
In the field of wound care, there exist several general categories of commonly used dressings, some of which aggressively adhere to a wound surface. For example, conventional gauze integrates into the wound as healing occurs and eschar forms on the wound surface. Other types of dressings are designed to adhere to the surrounding intact tissue around the wound site but not directly to the wound. However, such dressings often become dislodged or otherwise require frequent replacement during the healing process. As the dressings become dislodged or are replaced during dressing changes, the fragile epithelium can easily be damaged. Moreover, in the case of acute and chronic wounds, large amounts of exudate are typically produced which makes the use of such conventional dressings inferior as they generally do not properly manage wound exudate.
Placental tissue grafts have also been used for such purposes. These grafts, sometimes referred to as fenestration grafts, have holes manually punched through portions thereof to allow exudate to flow from the wound while the remaining portion of the graft releases growth factors and other cytokines to facilitate healing. However, these manually generated fenestration grafts lack reproducibility, are subject to tears and rips along the holes which adversely impact the graft's integrity, and extra care must be taken to prevent contamination of one fenestration graft with material from another fenestration graft.
Accordingly, there is a need to provide a biocompatible wound dressing that minimizes wound damage during the healing process and that is capable of managing exudate to ensure wound healing. There is a further need to produce a wound graft in a manner that allows commercial production that avoids tearing and cross-contamination during the production process in a cost- and time-efficient manner.